Hydrostatic transaxles

ABSTRACT

An axle assembly has an internally disposed hydrostatic transmission and speed reducing gearing. An input shaft supported in the housing drives a variable-displacement hydraulic pump, the pump fluidly coupled to a fixed-displacement hydraulic motor, and the motor drivingly connected through the speed reducing gearing to an output axle shaft. The housing being formed by three housing members and joined together along a substantially planar and horizontally peripheral seam formed therebetween such that two of the housing members are to one side of the seam and join with the third housing element. Two internal chambers formed by the three housing elements where one chamber contains the hydrostatic transmission and the other chamber contains the speed reducing gearing. A connecting shaft spanning between the chambers to provide the power transmission link between the hydrostatic transmission and the speed reducing gearing.

Division of application Ser. No. 10/068,888, filed on Feb. 11, 2002, nowU.S. Pat. No. 6,607,462, which is a division of application Ser. No.09/550,793, filed on Apr. 17, 2000, now U.S. Pat. No. 6,346,059, whichis a division of application Ser. No. 09/166,924, filed on Oct. 6, 1998,now U.S. Pat. No. 6,076,428. Provisional Application No. 60/061,811,filed on Oct. 14, 1997.

DESCRIPTION OF THE INVENTION

This invention relates to hydrostatic transaxles which are now used inincreasing numbers for lawn care and other outdoor duties as thepreferred choice for power transmission drive lines in products such aslawn and garden tractors, pedestrian walk-behind mowers and snowblowers.

DESCRIPTION OF THE RELATED ART

Hydrostatic transaxles of the type currently sold in the marketplacerequire careful assembly and service practices in order to avoid certainproblems occurring that may result in lower than expected operationallife of the product. Hydrostatic transmissions operate most effectivelyand efficiently when they are constructed with exceedingly smallclearances between their reciprocating and sliding elements. Thetransmission of power by such hydrostatic transmissions has now becomewidespread and the attendant small fluid leakage loss from the internalpressurized circuit during operation which is inherent with this type ofspeed changing device is generally considered insignificant as theresulting retardation in vehicle speed most often goes largely unnoticedby the end user. Hydrostatic transmissions work well and have a long anduseful life so long as the level of contamination suspended in the powertransmission fluid remains low. High levels of contamination carried bythe power transmitting fluid can rapidly wear out the aforementionedfine clearances resulting in an increase in fluid leakage, especiallyduring high pressure operation.

It is therefore of paramount importance during both the initial assemblyprocess when the hydrostatic transaxle is built as well as at subsequentservice repair intervals, that the possibility of contamination enteringthe hydrostatic transmission and its surrounding fluid chamber beminimised. In simple terms, the chance for the hydrostatic transmissioncomponents being contaminated during handling on the assembly lines inthe factory recede as the number of components in the total assemblybuild is reduced. It follows therefore, that if the hydrostatictransmission could be fully assembled and sealed in the housing prior tothe reduction gearing and differential shaft components being added,there would be an advantage.

In the past, because hydrostatic transmissions were of theself-contained “bolt-on” type designed specifically to be fitted to aninterface provided on an exterior mounting face of a separate transaxlecontaining the reduction gear train, the possibility of contaminationentering the hydrostatic transmission was not an issue when some form ofa repair was needed in the separate transaxle drive train unit. Forexample, in the event that the hydrostatic transmission needed to bereplaced, this type of repair could be quickly undertaken just byremoving a few bolts in order to separate the unit from the transaxleand replace it with another unit. If on the other hand, a bearing orshaft seal needed to be replaced in the transaxle drive train, such arepair could be easily effected just by dis-assembly of the transaxleand without disturbing the internal components of the hydrostatictransmission which would stay in-place in their own housing. A typicaldesign of the so-called “bolt-on” self-contained “stand-alone” type ofhydrostatic unit for mating to a separate transaxle device is shown inEaton Corporation U.S. Pat. No. 5,234,321 incorporated herein asreference.

Due to improvement in the art during the past decade or so, the vastmajority of hydrostatic transmissions now in use are of the integratedtype whereby a common housing is used to surround both the hydrostaticelements as well as the speed reducing gearing (and differential whenrequired), typically as shown in FIGS. 3 through 5 in Thoma et al. U.S.Pat. No. 4,979,583 incorporated herein as reference. Although theimprovement of the “integrated” type over the earlier “bolt-onstand-alone” type of hydrostatic transmission and transaxle combinationhas provided significant economic benefits in terms of loweringmanufacturing cost of the drive line such that hydrostatic transmissionsare now better able to compete more effectively with mechanical-shiftgear transmissions, inconveniences can arise when repairs are needed.The consequence of shipping units back to the factory for repair is bothcostly and inconvenient for the vehicle owner.

Furthermore, in the event of a service agent electing to make the repairhimself, for example, a normally relatively simple repair involving thereplacement of a worn bearing or seal, it is at present a fact that thiswould first necessitate the splitting open of the transaxle housing inorder to gain access to those elements needing replacement. As suchaction results in the hydrostatic transmission components being exposedto what may well be a relatively unclean working environment, a distinctpossibility exists that the hydrostatic transmission might have becomecontaminated such the repair is only short lived. Consequently, theservice agent may elect to substitute the faulty unit with a brand newreplacement but this has the disadvantage of much additional expense forthe vehicle owner, especially if the existing hydrostatic transmissionor conversely, the original gear train components were considered by theagent to be in good and still usable condition. There therefore is aneed in the art for a new integrated hydrostatic transaxle that willallow simple repairs to be undertaken by the dealership on thenon-hydrostatic components without exposing the internally disposedhydrostatic transmission components to contamination.

With all known integrated hydrostatic transaxles currently sold, factorytesting can only take place once the transaxle is fully assembled as thehydrostatic portion as well as the geared portion are contained within asurrounding two-piece housing structure. In the event the factory testindicates that the hydrostatic transmission is not operatingsatisfactorily, repair and rectification can be both costly and timeconsuming as the complete housing must first be dismantled in order tobe able to replace deficient hydrostatic componentry. What is thereforeneeded in the art a new form of integrated hydrostatic transaxle inwhich the two types of power transmitting componentry within thecomplete product package are separate from each other such that thehydrostatic transmission can be tested and approved before the remainingnon-hydrostatic components are assembled in place. What is also neededis a new form of integrated hydrostatic transaxle allowing rectificationwork, when needed, to be speeded up and therefore more economic toperform. What is further needed is a new solution whereby the amount ofhanding required during assembly on the assembly lines is minimisedbefore the hydrostatic transmission is fully sealed within thesurrounding housing structure.

As integrated hydrostatic transaxles of the type currently available inthe market require a large housing structure for containing bothhydrostatic and non-hydrostatic components, the machine tools needed toperform finish machining operations on the housing are expensive due totheir size. There would be a saving in machine tooling investment if thesize of transaxle housing were smaller in size, and there would befurther saving in terms of economies of scale if one part of the housingstructure of the hydrostatic transaxle could be used for numerous otherproduct types. What is therefore needed is a new form of integratedhydrostatic transaxle having a relatively small housing componentrequiring machining for the mounting of the hydrostatic transmissionsuch that the remaining and larger housing members required forcompletion of the transaxle housing structure can be used in theiras-received die-cast condition. What is further needed is a universalcover housing element for the mounting of the hydrostatic transmissionsuch that the sub-assembly can be used in combination with any number ofdifferent case housing elements to satisfy a range of products types.

SUMMARY OF THE INVENTION

From one aspect the invention consists in a housing structure for ahydrostatic transaxle where the housing construction comprising threehousing elements that inter-relate to form separate chambers for thehydrostatic transmission components and the geared components. An inputshaft is supported in the housing and extends into the chambercontaining the hydrostatic transmission to drive the hydraulic pump. Anoutput shaft is also supported in the housing and extends into thatchamber containing the geared components. In instances when a mechanicaldifferential is also located within the chamber containing the gearedcomponents, the output shaft then comprises two shafts that extend fromthe differential in opposite directions. Within the chamber containingthe geared components, the output shaft or shafts is drivingly engagedto the speed reduction gears and where the gears are driven by aconnecting shaft that forms the power transmitting link between thehydraulic motor in the hydrostatic chamber and the geared components inthe gear chamber.

By this invention, the hydrostatic transmission components for thehydrostatic transaxle can be assembled in a clean room and tested beforethe complete sub-assembly containing the hydrostatic transmission isdispatched to another location where the non-hydrostatic components areadded. As the hydrostatic sub-assembly is sealed by the surroundinghousing before entering the final assembly production lines, there is nochance for the hydrostatic transmission to become contaminated when theremaining components are added. In instances when the transaxlemanufacturer elects to sub-contract the task of building the completehydrostatic transmission to an outside agency, the supplied hydrostaticsub-assembly can be received in a ready-to-use condition therebyavoiding any need for the transaxle manufacturer to undertake inspectionprocedures to ascertain that the received goods are free fromcontamination from shipping and handling.

It is therefore an object of the invention to provide an improvedhousing for a hydrostatic transaxle whereby the chamber for thehydrostatic transmission components is segregated from that chambercontaining the speed reducing geared components in a manner whereby thehydrostatic transmission can be tested and approved before the remainingassembly involving the geared components takes place. It is a furtherobject of the invention to provide an improved housing for a hydrostatictransaxle whereby the service life of the unit can be extended byallowing simple repairs to be effected in the field without disturbanceor disassembly of the hydrostatic transmission components.

What is further needed in the art is a new form of integratedhydrostatic transaxle in which a relatively small housing componentstructured for carrying the hydrostatic transmission be provided with anability to resist and absorb within its structure the fluid pressuregenerated loads by the hydrostatic transmission such that the remainingand larger housing members of the hydrostatic transaxle serve to supportthe non-hydrostatic loads. It is a further object of the invention togroup all the machining operations for the housing structure of thehydrostatic transaxle into said smallest of the three housing elementsthereby providing material saving in tooling investment and totalmachining hours required.

It is a further object of the invention to segregate the hydrostatictransmission from the reduction gearing by providing a case housingelement with a substantially planar and horizontally peripheral seamserving as an abutment surface onto which interface two smaller sizedcontainer-shaped housing elements whereby the power transmission linkconnecting the hydrostatic transmission to the reduction gearing has anaxis of rotation arranged in parallel relationship with regard to theseam and where the housing elements serve to protect the powertransmission link from corrosion or falling debris such as grasschippings which commonly accumulate on the exterior surface ofhydrostatic transaxle apparatus.

In one form thereof, the hydrostatic transaxle of the inventioncomprises an axle assembly having a housing including first, second andthird housing elements joined along a substantially planar andhorizontally peripheral seam formed therebetween such that the first andsecond housing elements are to one side of the seam; the third housingelement being provided with first and second cavities and where thefirst cavity is closed by an opposite cavity provided by the firsthousing element to define a first chamber. The second cavity is closedby an opposite cavity provided by the second housing element to define asecond chamber; a hydrostatic transmission comprising avariable-displacement pump and fixed-displacement motor disposed withinthe first chamber and speed reducing gearing disposed within the secondchamber; at least one outwardly extending output power transmissionshaft rotatably mounted in the housing and an input power transmissionshaft rotatably mounted in the housing and operatively connected to thepump, the hydraulic motor being operatively connected to the outputpower transmission shaft by means of the speed reducing gearing, andwhere a connecting shaft spans across from the first chamber to enterthe second chambers to provide the power transmission link between thehydrostatic transmission and the speed reducing gearing.

Although the preferred shaft mounting location shown in this inventionfor the mechanical drive connection from the hydraulic motor to theprojecting axle output is disposed along the seam whereby all threehousing elements provide support surfaces in the form ofsemi-cylindrical pockets, an alternative embodiment is disclosed wherebysuch support surfaces are disposed fully to one side of the seam. Anadvantage of this alternative embodiment is that it allows at least oneof the three housing elements to have a substantially flat profile atthe peripheral seam, for instance the gear housing element, and wherethis housing element may manufactured in various materials such as analuminium alloy casting; a pressed-steel component or as a simpleplastic or nylon moulding.

In the embodiments described below, the fluid pressure generated loadsby the hydrostatic transmission are easily absorbed and contained withinthe smallest of the three housing elements while the power transmissionlink between the hydraulic motor in the hydrostatic chamber and thegeared components in the gear chamber provide hitherto unattainableimprovements and savings in terms of assembly and repair practices overthe integrated hydrostatic transaxles types presently on the market.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other novel features and objects of theinvention, and the manner of attaining them, may be performed in variousways and will now be described by way of examples with reference to theaccompanying drawings, in which:

FIG. 1 is a part-sectioned side view of the transaxle according to theinvention.

FIG. 2 is a plan view of the case element along the section line I—I ofFIG. 1.

FIG. 3 is a view of the hydrostatic transmission as it is mounted in thetransmission cover element according to the invention.

FIG. 4 is a view of the transmission cover element and hydrostatictransmission along the section line II—II of FIG. 4.

FIG. 5 is a view of the hydrostatic transmission located within theinternal chamber formed between the case and the transmission coverelement.

FIG. 6 is a view of the hydrostatic transmission and a portion of thegear reduction located within their respective internal chambers formedbetween the case and the transmission cover element.

FIG. 7 is a plan view of the gear cover element showing its interiordetails.

FIG. 8 is a view of the hydrostatic transaxle according to a furtherembodiment of the invention.

FIG. 9 is a side view of the hydrostatic transaxle along the sectionline III—III of FIG. 8.

FIG. 10 is a plan interior view of the gear cover element of FIGS. 8 and9.

FIG. 11 shows an alternative mounting arrangement on the case for fixingthe hydrostatic transaxle to a frame or chassis.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The housing for the hydrostatic transaxle 1 can be comprised of at leastthree housing elements, the main housing element being here called thecase 2, the largest of the three housing elements being provided with amounting face 3 and which surrounds two cavities 4, 5 sunken from thesurface. The first cavity 4 provides internal space for the location ofthe hydrostatic transmission 7 whereas the second cavity 5 provides thespace for the location for various elements comprising the speedreducing gearing 6 and mechanical differential 8. A number ofsemi-circular pockets are also provided on the mounting face to supportvarious shafts and bearings, for instance, pockets 10, 11 for the outputtransmission shaft, which as shown here comprise two output axletransmission shafts 12, 13.

A transmission cover element 15 and a gearing cover element 16 areattached against the case 2 on this mounting face 3, these covers 15, 16being attached to the case 2 by screws or bolts. For instance, shown area series of holes 17 on mounting face 3 of case 2 which are arranged tosurround first cavity 4 into which screws 20 engage. A second series ofholes 18 are also included on mounting face 3 of case 3 which arearranged to surround second cavity 5 into which screws 21 engage. Allsuch holes 17, 18 are preferably cast as slightly tapered blind holes sothat self-threading screws are used transmission cover element 15 andgeared cover elements 16 respectively to the case 2.

The mounting face 3 on case 2 is the horizontal peripheral seam thatsurrounds both the first and second cavities 4, 5 and where, in thisfirst embodiment, the axle output transmission shafts 12, 13 have theiraxis of rotation substantially coincident with the seam. Thetransmission cover element 15 and gear cover elements 16 abut againstthe seam/mounting face 3 of the case 2 along a parting plane as shown inFIG. 1.

As shown in FIGS. 1 and 3, the shape of the transmission cover element15 is substantially in the form of a container such that it has a cavity25 into which a portion of the hydrostatic transmission 7 extends into,and where a number of mounting surfaces are included, such as shown asbosses 26, 27 to which part of the hydrostatic transmission 7 can beattached. Preferably, the hydrostatic transmission is mounted to thecover element 15 rather than to the case element 2 to obtain maximumbenefit of this invention, although it could also possible to mount someor all of the hydrostatic transmission components in the case 2, andpossibly then the input shaft driving the pump of the hydrostatictransmission would be supported by bearings provided in the case element2.

As shown, at the open-end of the container of transmission cover element15, a surrounding radially outwardly extending base flange 28 isprovided and where a plurality of holes 29 are included on this flangeor lip 28 so that attachment screws 20 can pass through holes 29 andextend beyond its mounting surface 30 and engage with holes 17 providedon the case 2 that surround the first cavity 4. The bottom surface offlange 28 is therefore the mounting surface 30 of the transmission coverelement 15 which interfaces with the mounting surface 3 provided on thecase 2. At this interface, sealing compound of the anaerobic type isused on the interface so that the internal chamber 33 which is formed bycavities 4, 25 in the case 2 and transmission cover element 15respectively, into which is housed the hydrostatic transmission 7 andits operating fluid, is separated and protected from the outer exteriorenvironment of the transaxle 1. Internal chamber 33 is flooded withhydraulic fluid which acts as the power transmitting medium for thehydraulic pump 35 and motor 36 of the hydrostatic transmission 7, andwhere chamber 33 is connected by passage 38 in the vertical wall 39 oftransmission cover element 15 so that expansion and contraction of thefluid volume in chamber 33 can take place by spilling the excess amountinto an auxiliary chamber 40 provided by header tank 41 here shownattached to the transmission cover element 15.

As best shown in FIG. 2, cavity 5 in case element 2 is provided with anumber of semi-cylindrical pockets 51, 52, 53, 54 to carry a number ofbearings which provide the support for shafts 60, 61 on which variouselements of the speed reduction gear train 6 are mounted. Furtherpockets 203, 204 are provided in case element 2 for the positioning ofbearing 191 and seal 193 respectively as shown in FIGS. 5 and 6. Theshape of the gear cover element 16 is also generally in the form of acontainer. FIG. 7 being a plan view and shows it having severalsemi-cylindrical pockets such as pockets 63, 64 that correspond withpockets 51, 52 in case 2, whereas pockets 66, 67 for intermediary shaft61 correspond with pockets 53, 54 in case 2. Pockets 68, 69 for axleoutput shafts 12, 13 correspond with pockets 10, 11 in the case 2, andwhere bearings 70, 71 are used to support respective shafts 12, 13.

As best seen in FIGS. 1 and 7, surrounding cavity 50 of cover element 16at the mounting surface 74 is an outwardly radially extending flange 75where a plurality of holes 77 are included on flange 75 allowingattachment screws 21 to pass through and engage with their correspondingholes 18 provided in case 2 that surround the second cavity 5. Thebottom of the flange is therefore the mounting surface of the gear coverelement which interfaces with the mounting surface provided in the case2. At this interface, sealing compound is use so that the internalchamber 80 created by the second cavity 5 in the case 2 and the cavity50 in the gear cover element 16 is isolated from the exterior of thetransaxle 1.

The hydrostatic transmission 7 used to best illustrate the advantages ofthis invention is preferably mounted to the transmission cover element15 prior to that element being attached to the case 2. An input shaftsupported by bearings 101, 102 in the transmission cover element 15 isoperatively connected to the pump of the hydrostatic transaxle 1, andwhere a rotary shaft seal 103 is fitted about the input shaft 100 isprevent fluid from chamber 33 escaping. Although the input shaft 100could be arranged to directly drive the pump 35 if so desired oralternatively, input shaft 100 can be operatively connected to the pump35 by means of gears which may be of the bevel type as is shown or spurgears. Bevel pinion 107 is fixed to shaft 100 and meshes with bevel gear108 to drive the cylinder-barrel 110 of the pump 35. Bevel gear 108 isfixed to cylinder-barrel 110 of the pump so to rotate at equal speed,and where the barrel 110 is supported for rotation on pintle-valve 112,pintle-valve 112 being provided with internal fluid passages 113, 114 sothat fluid from barrel 110 can flow to the cylinder-barrel 115 of thehydraulic motor 36.

Although the form of hydrostatic transmission here used to describe theinvention is of a type using a radial array of cylindrical rollers,other forms of fluid displacement machines may also be used, forexample, those having pistons with slippers or even ball pistons.Furthermore, the hydrostatic transmission as here described has a pumpand motor arranged in co-axial back-to-back relationship, but ahydraulic right-angle fluid connection could also be used in which therotational axes of the pump and motor is perpendicular, and therebyremoving the need to include bevel gearing.

Barrel 110 of the pump 35 is provided with a plurality of radiallyarranged cylinders 117 which are a fixed axial distance relative to thearcuate shaped slots 118, 120 provided on the pintle-valve 112. Eachcylinder 117 includes a port 119 which matches with arcuate slots 118,120 during rotation of barrel 110. Each cylinder 117 receives a piston122 to which a roller 123 is mounted on its outer end and where therollers 123 operate against a surrounding annular track-ring 125. Thebarrel 115 of the hydraulic motor 36 is likewise provided with aplurality of cylinders 126 which are a fixed axial distance relative tothe arcuate shaped slots 127, 128 provided on the pintle-valve 112. Eachcylinder 126 includes a port 130 which matches with arcuate slots 127,128 during rotation of barrel 115, and each cylinder 126 receives apiston 131 and a roller 132 is mounted on the outer end of each piston131 and where the rollers 132 operate against a surrounding annulartrack-ring 133. In the case of the hydraulic motor 36, track-ring 133 iseccentrically positioned with respect to the pintle-valve 112 whereas inthe case of the hydraulic pump 35, track-ring 125 is pivotable aboutpivot pin 135. Control-shaft 136 is connected to track-ring 125 by linkpins 138, 139 in order that the eccentricity of track-ring 125 can bevaried relative to the longitudinal axis of the pintle-valve 112.

The control shaft 136 is supported between a pair of semi-cylindricalpockets 140, 141 provided on the mounting surface 30 of the transmissioncover element 15 and a complementary pair of pockets 142, 143 providedon the mounting surface 3 of the case 2. A rotary seal 145 is positionedwithin a further pair of pockets 146, 147 to surround control-shaft 136and prevent the escape of hydraulic fluid from internal chamber 33.

As shown in FIG. 1, in the interior cavity 25 of the transmission coverelement 15, inwardly projecting bosses 26, 27 mounting are spot faced inorder to provide a datum and thereby an accurate mounting surface forthe hydrostatic transmission 7. During the same machining operation, thevertical hole 153 is sized for both the shaft bearings 101, 102 andfluid seal 103.

Located in the space between the barrels 110, 115, the pintle-valve 112and pivot pin 135 are clamped between a two-piece sub-frame 160, 161which can then be attached by screws 162 to the machined mountingsurfaces on the bosses 26, 27. Holes or slots (not shown) in bothsub-frame elements 160, 161 allow the passage of these fastening screws162 which are received into threaded holes provided within the bosses26, 27 in the transmission cover element 15. When the sub-frame 160, 161is located onto bosses 26, 27, the action of tightening screws 162results that sub-frame elements 160, 161 are pressed together while atthe same time clamping the pintle-valve 112 and pivot pin 135 in placesuch that the hydrostatic transmission is fixedly secured against themounting surface provided in transmission cover element 15.

A second sub-frame 165 in the form of a pressed steel “L” shaped platemay also be used to secure the hydrostatic transmission to thetransmission cover element 15 as shown in FIGS. 3 and 4. One arm shownas 166 of sub-frame 165 is provided with an aperture 167 through whichthe end of the pintle-valve 112 protrudes through. That portion at endof the pintle-valve 112 which is inserted through aperture 167 mightvery well be ground with an outer profile conducive to causing thematerial of arm 166 adjacent to aperture 167 to deform slightly as theend of the pintle-valve is passed through before deforming back to holdtight when it reaches the correct resting place on the pintle-valve.Likewise, a further aperture 169 is included through which the pivot pin135 protrudes through. The arm or base 170 of sub-frame 165 is providedwith two holes (not shown) through which fastening screws 174 passthrough, and where the base 170 rests on a machined surface 175 on theinterior of the transmission cover element 15. Once screws 174 aretightened, base 170 is fastened to mounting surface 175 and thus,sub-frame 165 and hydrostatic transmission becomes fixedly held to thetransmission cover element 15.

As shown in FIG. 4, motor track-ring 133 is attached to the centralsub-frame 160, 161 by way of pins 180, 181 that extend from end face 182of track-ring 133 and engage between respective pairs of pockets shownby dotted lines 184, 185 provided on the interface between sub-frameelements 160, 161. The pins 180, 181 and thereby track-ring 133 becomelocked in position once screws 162 holding the sub-fame 160, 161 to themounting surface bosses 26, 27 are tightened.

Therefore, once both sub-frames 160, 161, 165 are fastened totransmission cover element 15, the hydrostatic transmission 7 held inposition within chamber 33.

The shaft 190 connecting with the hydraulic motor 36 is built-up as asub-assembly with its support bearings 191, 192 and seal 193, and wherea drive coupling 195 is used top connect shaft 190 to motor barrel 115.Anaerobic sealant is applied on the surfaces of semi-cylindrical pockets200, 201, 202 in the transmission cover element 15 before the shaftsub-assembly is moved into position in element 15.

The transmission cover element 15 with its attached hydrostatictransmission 7 is then lowered over cavity 4 in the case 2 as shown inFIG. 5. The mounting surface 3 on the case 2 has anaerobic sealingcompound applied, and once in place, the series of screws 20 passthrough the holes 29 of the radially extending flange 28 or lip to beengaged into holes 17 in case 2 so that case 2 and cover 15 are tiedtogether as a unitary housing structure. Thus the complete hydrostaticsub-assembly is complete and ready to be tested once transmission fluidhas been poured into the internal chamber 33. Once the test is over, thehydrostatic sub-assembly is ready for dispatch so that the remaininggear and other components can be added before the gear cover element 16and case 2 are locked together by screws 21.

A mechanical disengage mechanism is sometimes useful in hydrostatictransaxles when it is desired to manually push the vehicle withoutoperating the engine that is normally is used to drive the transaxle andpropel the vehicle. As here disclosed, this can be easily achieved byhaving a gear 211 fixedly mounted to a brake shaft 60 in order that amechanical disengage mechanism can be incorporated between shafts 190,60.

A collar element 212 is used to connect respective shafts 190, 60together by means of spline connections 213, 214. Lever means (notshown) act in groove 215 on collar element 212 to shift the collarslightly to the left so that the spline 213 connection is no-longerengaged to motor shaft 190 so that shafts 190, 60 are no-longerconnected together to rotate at equal speed. A parking brake 217attached to shaft 60 ensures the vehicle can be arrested during periodswhen shafts 190, 60 remain disconnected. Shaft 60 is supported in abearing 220 seated between semi-cylindrical pockets 52, 64 provided incase 2 and gear cover element 16 respectively, and also journalled atits inner end 225 in a hollow 226 provided in shaft 190.

However, it should be noted that if no mechanical disengage is required,or when an alternative method is used to obtain the same effect, forinstance, through the incorporation of a mechanism whereby the fluid inthe hydrostatic fluid circuit between the pump and motor isshort-circuited, there would be no need to use two shafts such as 60,190. Instead, a single shaft could be used which would connect thecylinder barrel 115 of the motor 36 to the pinion gear 211 so that poweris transmitted from the barrel 115 to the gear 211. In either casehowever, the shaft or shafts connecting the hydraulic motor 36 to thegear reduction train 6 for the purposes of definition for this inventionis called the power transmission link.

Prior to the assembly into the case 2 of the non-hydrostatic elementssuch as shaft 60, anaerobic sealing compound is applied to the mountingsurface 3 as well as to all the semi-cylindrical pockets such as pocket52. Thus then all the remaining components such as brake-shaftsub-assembly, speed reducing gearing and the differential (when used)together with the output axle shaft or shafts can be lowered intoposition in the case 2. As depicted, the speed reducing gearing 6comprises a pinion gear 211 splined 228 to brake shaft 60 which mesheswith a gear 230 fixed on an intermediate shaft 61. Intermediate shaft 61has a further gear 231 fixed to it which meshes with the ring gear 233that comprises as shown part of the differential unit 8. Thedifferential 8 shown is of the type that has four bevel gears 235, 236,237, 238, two of which 236, 238 are attached to respective axle outputshafts 12, 13 that extend out from the chamber 80. For thoseapplications where there is no requirement to have a differentialeffect, shafts 12, 13 would in effect be a single shaft. Gear 233 wouldbe modified so to omit bevel gears 235, 236, 237, 238 and be fixed tothe output shaft. The output shaft would still protrude from the case 2and cover 15 on both sides or only on one side to suit the application.

As shown in FIG. 2, bearings 240, 241 are provided for the intermediateshaft 61 which sit in pockets 53, 54 in case 2 and pockets 66, 67 ingear cover element 16.

It is a feature of the invention that both cover elements 15, 16 engageon the same bridging element, the example used to illustrate this beingcylindrical bearing member 192, this being accomplished by cylindricalbearing member 192 spanning the semi-cylindrical pockets 202, 63provided in the otherwise separate cover elements 15, 16. As a result,motor shaft 190 and brake shaft 60 are not exposed to the exterior ofthe transaxle even though the pairs of cavities 4, 25 and 5, 50 creatingrespective chambers 33, 80 for the hydrostatic transmission 7 and speedreducing gearing 6 are separate from each other. It should be notedhowever, especially for instance, were shafts 190, 60 combined into asingle shaft, that a rotary seal member could perform as a bridgingelement in place of a cylindrical bearing member. In that modification,the seal would ideally be pressed into a cylindrical sleeve, and wherethe sleeve would fit in pockets such as pocket 51 in case 2 and pockets202, 63 in respective cover element 15, 16. Be the bridging element aseal or a bearing or just an empty sleeve, anaerobic sealant would besmeared at the interface where the bridging element is in engagingcontact with the pockets in the housing so that external moisture orcontamination is unable to enter chambers 80, 33. For ease andconvenience, the outer profile for the bridging element best suited toaccomplish the task is cylindrical as depicted but the outer profilecould be modified, for instance to being square, and still work.

Therefore, whatever component is chosen to span the gap between the twocover housing elements 15, 16 about the power transmission link betweenthe hydraulic motor portion and the gear portion of the hydrostatictransaxle, the advantage of being able to segregate chambers 33 from 80from each other as well as isolate said chambers from the externalenvironment of the hydrostatic transaxle is intended to fall within thescope of the claims. Furthermore, it is also intended that thisinvention cover an arrangement whereby the power transmission linkspanning chambers 33, 80 is not protected by any bridging element atall, and where in that arrangement a portion of the connecting shaft orshafts comprising the power transmission link would be exposed to theouter environment of the hydrostatic transaxle. In that respect,provided two rotary seals are applied on the connecting shaft, each sealbeing located adjacent the interface between respective cover elementsand the case element, no contamination can enter chambers 5, 33. If theexposed portion of connecting shaft is lying downward in orientation,then debris and dust is unlikely to collect in the small gap that islikely to exist between the connecting shaft and housing.

Once all the gear train elements are in place, anaerobic sealingcompound is applied over those seal and bearing elements whichinter-relate with pockets provided in the gear cover element 16. Thengear cover element 16 is placed in position over the cavity 5 of thecase 2 before screws 21 are inserted through holes 77 to engage withblind holes 18. Once screws have been tightened, case 2 and gear cover16 elements are thus firmly together.

To operate the hydrostatic transaxle 1, when track-ring 125 of the pump35 is moved by control-shaft 136 into an eccentric position relative tothe pintle-valve 112, and during rotation of barrel 110 by the inputshaft 100, the pistons 122 reciprocate radially within their respectivecylinders 117 and fluid inside the cylinders 117 is displaced throughport 119 and flow takes place between arcuate shaped slots 118, 120. Thefluid in passages 113, 114 enters the motor 36 through arcuate shapedslots 127, 128 into cylinders 126 in barrel 115 by way of ports 130. Thefluid entering each cylinder 126 causes pistons 131 to reciprocate andthrough the relationship to the eccentrically positioned track-ring 133,and thereby barrel 115 is caused to rotate. Barrel 115 being connectedto shaft 190 by coupling 195 cause shafts 190, 60 of the powertransmission link to rotate at equal speed, and power is transmitted bygear 211 fixed to shaft 60 to the remaining elements of the speedreducing means 6 for the purpose of torque multiplication to thetransmission output shaft or axle shafts 12, 13.

In the second embodiment of the invention as shown in FIGS. 8 to 10, thetwo main difference over what has already been described for the firstembodiment is that the rotational axes of the power transmission link aswell as the other shafts on the gear reduction compartment are no-longercoincident with the peripheral seam but are now lying offset to one sideof the seam; and secondly, the mounting surfaces provided in the housingonto which the hydrostatic transmission components are fixed are nowlying on the peripheral seam. The housing structure of the hydrostatictransaxle comprises a main housing case 251 and two smaller housingcover elements, 252, 253. Cover element 252 includes the mountingsurfaces 270, 271 for attachment of the hydrostatic transmissioncomponents whereas gear cover element 253 is a form a blanking platewith protuberances where necessary.

The axle output shaft(s) 256 and the other shafts required for speedreduction from the hydrostatic transmission such as the powertransmission link shafts 254, 255 are here shown located belowperipheral seam or parting-plane 2 50. In this respect, sub-surfacebearing carriers, here called inserts are needed such is shown in FIG. 9by way of example as insert 260. Insert 260 is fitted into a channel asshown 290 provided in the case element 251 and is arranged so that itstop surface 261 is level with the peripheral seam 250. The peripheralflat portion 291 of gear cover element 253 that lies directly above thetop surface 261 of insert 260 acts to lock and hold insert 260 in placewithin the channel 290.

Further inserts similar to the type 260 are used for shafts 254, 255 andthe intermediary shaft (not shown), shafts 255 being connected to outputshaft(s) 256 by the type of gearing already described for the firstembodiment.

As shown in FIG. 8, various bearings and seals such as bearings 273,275, 276 and seals 274, 277 are located within respectivesemi-cylindrical pockets 280, 282, 283 and 281, 284 provided in the casehousing element 251. All these bearings and seals are positioned byinserts so that they are sunken from the surface of the parting-plane250 to lie in case element 251. For instance, insert 300 is provided forbearings 273, 275 and seal 274, and where the flat top surface 301 ofinsert 300 abuts with the flat junction surface 302 provided in thetransmission cover element 252. Inserts 305, 306 are similarly used, buthere they lie between the case element 251 and the flat portion 291 ofgear cover element 253.

The gear cover element 253 shown in FIG. 10 can be generally flat inprofile about its peripheral seam 292 adjacent to where the mountingholes 293 are located, but includes a central cavity marked as 294 thatwhen viewed from the side, would be bulge shaped to provide thereby roomfor the various gears and differential that partially extend across theparting plane 250 into cavity 294 when elements 251, 253 become attachedtogether. Screws 296 are shown locking the peripheral flat portion 291of gear cover element 253 to the case element 251.

As the various shafts such as 254, 255, 256 are now located buriedwithin the structure case element 251 and not withstanding those forcesand loads tending in the direction towards the gear cover element 291,the bulk of the mechanical loads are absorbed in the case element 251.Therefore gear cover element 291 is subjected to less loads than in thefirst embodiment such that for certain light-duty applications can bemanufactured as a simple and inexpensive steel pressing or plastic/nylonmoulding to thereby provide further worthwhile savings in the overallmanufactured cost of the hydrostatic transaxle.

FIG. 11 differs only very slightly from the hydrostatic transaxle shownin the previous embodiments of the invention in order to show that thecase element 320 may have groups of upwardly extending external mountingbosses 321 and 322 that extend above the gear cover element 323 adjacentto respective axle output shafts 12, 13. All the bosses contain athrough-hole 325 so that the case element 320 can be bolted to theunderside frame or chassis of the vehicle.

For many applications, it is most advantageous that the input shaft forthe hydrostatic transaxle be located in the transmission cover elementas shown in the embodiment illustrated. However, should it becomeadvantageous to locate the input shaft in what before was depicted asthe case element, then the above described embodiments would be adaptedso that the hydrostatic transmission is attached to mounting surfacesprovided in the case rather then in the transmission cover element.Equally, the hydrostatic transmission and geared components could eachbe located within two separate cavities provided in a single coverhousing element and where now two separate case elements would be used,one case element having a cavity for the hydrostatic transmission andthe other case element having a cavity for the geared components. Withthis re-arrangement of the housing parts, respective pairs of cavitiescombine to form chambers, one chamber for the hydrostatic transmissionand another but distinctly separate chamber for the geared components.In all variations with the housing construction, the power transmissionlink spanning that chamber containing the hydrostatic transmission tothe other chamber containing the reduction gearing and differentialwould still be needed.

Although a radial piston hydrostatic transmission has been illustratedfor the purpose of describing this invention, an axial pistonhydrostatic transmission may also be used to good effect. In the axialpiston type of hydrostatic machine, the centre section that containswithin it the fluid passages connecting the hydraulic pump to thehydraulic motor, by incorporation with this invention be attached to thetransmission cover element is a similar manner as the sub-frames heredescribed for the radial piston embodiments. Alternatively, the centresection could be attached near to the bottom surface of the cavity in acase element in a manner whereby a similar transmission cover elementand a geared cover element is used in combination with the case as hasalready been described for the embodiments chosen to best explain theinvention. As a further alternative, the axial piston hydrostatictransmission may be mounted to the exposed surface on a cover elementhaving separate cavities for the hydrostatic transmission and gearingelements. In this arrangement the center section would act as thetransmission case element by enclosing the cavity in the cover to createthe internal chamber for the hydrostatic transmission. In a designhaving the axial piston form of hydrostatic transmission, it would alsobe possible to mount the centre section or even the swash-plate of thepump directly adjacent to where the input drive shaft enters the housingstructure of the hydrostatic transaxle. However, in all such variations,a power transmission link is required to connect the motor of thehydrostatic transmission in the one chamber to the reduction gearing anddifferential located in the other chamber.

It is to be understood that while we have illustrated and describedvarious embodiments of our invention, it is not to be limited to any onespecific form or arrangement of parts herein described and shown exceptinsofar as such limitations are included in the claims.

1. An axle assembly comprising a hydrostatic transmission and adifferentialled gear reduction transmission disposed adjacent oneanother within respective chambers formed by at least three surroundinghousing elements, said hydrostatic transmission including a hydrostaticpump and motor and said differentialled gear reduction transmissionincluding a reduction gear train comprising a plurality ofinterconnecting gears, said hydrostatic transmission having pump andmotor cylinder barrels fluidly connected together, and said motorcylinder barrel connected to said reduction gear train by a powertransmission link having a horizontal axis of rotation disposed in afirst horizontal plane and comprising a motor output shaft and areduction gear train input shaft, said motor shaft having first andsecond respective ends, said first end disposed in said hydrostaticchamber and connected to said motor cylinder barrel, said second endconnectable to said reduction gear train input shaft, said first andsecond respective ends being surrounded by said at least threesurrounding housing elements, wherein two of said at least threesurrounding housing elements reside side by side one another on one sideof said first horizontal plane.
 2. The axle assembly according to claim1 wherein those remaining of said at least three surrounding housingelements not disposed to said one side of said first horizontal planeare arranged to reside on the opposite side of said first horizontalplane.
 3. The axle assembly according to claim 2 wherein said at leastthree surrounding housing elements are respectively provided withuniplanar junction seams meeting at a common parting plane arranged tobe coincident with said first horizontal plane.
 4. The axle assemblyaccording to claim 3 wherein two of said least three surrounding housingelements are upper cover housing elements.
 5. The axle assemblyaccording to claim 3 wherein two of said least three surrounding housingelements are lower case housing elements.
 6. The axle assembly accordingto claim 3, and further comprising an input drive shaft having avertical axis of rotation rotatably supported in one of said at leastthree surrounding housing elements, said vertical axis of rotation ofsaid input drive shaft disposed perpendicular to said first horizontalplane, wherein said input drive shaft comprises a first portionprotruding outside of the respective housing element and a secondportion protruding inside of said respective housing element todrivingly engage said pump.
 7. The axle assembly according to claim 6,and further comprising a pair of axle shafts rotatably supported in atleast two of said at least three housing elements, said axle shaftshaving a horizontal axis of rotation disposed parallel with said firsthorizontal plane.
 8. The axle assembly according to claim 7 wherein saiddifferentialled gear reduction transmission further comprising amechanical differential drivingly connected to said axle shafts.
 9. Theaxle assembly according to claim 8 wherein said horizontal axis ofrotation of said axle shafts is coincident with said first horizontalplane.
 10. The axle assembly according to claim 8, and furthercomprising interior mounting surfaces disposed on a second horizontalplane in at least one of said at least three housing elements; saidhydrostatic transmission further comprises a pintle-valve orcentersection equivalent for fluidly coupling said pump and motortogether, said pintle-valve or centersection equivalent fixed to saidinterior mounting surfaces, wherein said second horizontal plane residesparallel to and not coincident with said first horizontal plane and saidsecond horizontal plane positioned nearer said first portion of saidinput drive shaft than said first horizontal plane.
 11. The axleassembly according to claim 10 and further comprising a bulkhead wallprovided by at least one of said at least three surrounding housingelements, said bulkhead wall formed substantially vertically to bedisposed generally parallel to the vertical axis of said input driveshaft, said bulkhead wall delimiting an inner fluid reservoirsurrounding said hydrostatic transmission from an inner fluid reservoirsurrounding said differentialled gear reduction transmission such thatsaid hydrostatic transmission is disposed one side of said internalbulkhead wall whereas said differentialled gear reduction transmissionis disposed on the opposite side.
 12. The axle assembly according toclaim 11 wherein only two of said at least three surrounding housingelements are aluminium pressure die-castings.
 13. The axle assemblyaccording to claim 10 wherein said motor output shaft is piloted to saidgear reduction train input shaft, the piloting of said motor outputshaft and said gear reduction train input shaft constituting thealignment mechanism of said power transmission link.
 14. The axleassembly according to claim 1 wherein any two of said at least threesurrounding housing elements are aluminium pressure die-castings. 15.The axle assembly according to claim 14 wherein the remaining at leastone of said at least three surrounding housing elements is a pressedsteel component.
 16. The axle assembly according to claim 14 wherein theremaining at least one of said at least three surrounding housingelements is a plastic or nylon moulding.
 17. An axle assembly comprisinga hydrostatic transmission and a differentialled gear reductiontransmission disposed within at least three surrounding housingelements, said hydrostatic transmission including a hydrostatic pump andmotor and said differentialled gear reduction transmission including areduction gear train comprising a plurality of interconnecting gears,said hydrostatic transmission connected to said reduction gear train bya power transmission link having a horizontal axis of rotation disposedin a first horizontal plane and comprising a motor output shaft and areduction gear train input shaft, a user operated mechanical disconnectmechanism for selectively disengaging said motor output shaft from saidreduction train input shaft; a bridging element surrounding said motoroutput shaft and disposed adjacent said mechanical disconnect mechanism,wherein at least two of said at least three surrounding housing elementsreside side by side one another on one side of said first horizontalplane and wherein those remaining housing elements of said at leastthree surrounding housing elements not disposed to said one side of saidfirst horizontal plane reside on the opposite side of said firsthorizontal plane, said at least three surrounding housing elements arerespectively provided with uniplanar junction seams meeting at a commonparting plane coincident with said first horizontal plane.
 18. The axleassembly according to claim 17, wherein said two of said least threesurrounding housing elements are housing cover elements, and where eachhousing cover element overlies a respective end of said bridgingelement.
 19. The axle assembly according to claim 17, wherein said twoof said least three surrounding housing elements are housing caseelements, and where each housing case element overlies a respective endof said bridging element.
 20. The axle assembly according to claim 21,and further comprising an input drive shaft having a vertical axis ofrotation rotatably supported in one of said at least three surroundinghousing elements, said vertical axis of rotation of said input driveshaft disposed perpendicular to said first horizontal plane, whereinsaid input drive shaft comprises a first portion protruding outside ofthe respective housing element and a second portion protruding inside ofsaid respective housing element to drivingly engage said pump.
 21. Theaxle assembly according to claim 20, and further comprising a pair ofaxle shafts rotatably supported in at least two of said at least threehousing elements, said axle shafts having a horizontal axis of rotationdisposed parallel with said first horizontal plane.
 22. The axleassembly according to claim 21 wherein said differentialled gearreduction transmission further comprising a mechanical differentialdrivingly connected to said axle shafts.
 23. The axle assembly accordingto claim 22 wherein said horizontal axis of rotation of said axle shaftsis coincident with said first horizontal plane.
 24. The axle assemblyaccording to claim 22, and further comprising a collar element disposedon respective ends of said motor output shaft and said reduction geartrain input shaft, said collar element having a locked axial positionwhere it is rotationally locked to said respective ends of said motoroutput shaft and said reduction gear train input shaft and an unlockedaxial position where it is rotationally locked to the end of only one ofsaid motor output shaft and said reduction gear train input shaft, saidcollar operationally connected to said user operated disconnect member.25. The axle assembly according to claim 22, and further comprising acollar element disposed on respective ends of said motor output shaftand said reduction gear train input shaft, said collar element shiftablein one axial direction for drivingly connecting said motor output shaftto said reduction gear train input shaft and in the other axialdirection for drivingly disconnecting said motor output shaft from saidreduction gear train input shaft, said collar operationally connected tosaid user operated disconnect member.
 26. The axle assembly according toclaim 22, and further comprising interior mounting surfaces disposed ona second horizontal plane in at least one of said at least three housingelements; said hydrostatic transmission further comprises a pintle-valveor centersection equivalent for fluidly coupling said pump and motortogether, said pintle-valve or centersection equivalent fixed to saidinterior mounting surfaces, wherein said second horizontal plane residesparallel to and not coincident with said first horizontal plane and saidsecond horizontal plane positioned nearer said first portion of saidinput drive shaft than said first horizontal plane.
 27. The axleassembly according to claim 26 and further comprising a bulkhead wallprovided by at least one of said at least three surrounding housingelements, said bulkhead wall formed substantially vertically to bedisposed generally parallel to the vertical axis of said input driveshaft, said bulkhead wall delimiting an inner fluid reservoirsurrounding said hydrostatic transmission from an inner fluid reservoirsurrounding said differentialled gear reduction transmission such thatsaid hydrostatic transmission is disposed one side of said internalbulkhead wall whereas said differentialled gear reduction transmissionis disposed on the opposite side.
 28. The axle assembly according toclaim 27 wherein only two of said at least three surrounding housingelements are aluminium pressure die-castings.
 29. The axle assemblyaccording to claim 26 wherein said motor output shaft is piloted to saidgear reduction train input shaft, the piloting of said motor outputshaft and said gear reduction train input shaft constituting thealignment mechanism of said power transmission link.
 30. The axleassembly according to claim 29 wherein said bridging element has a maleprofile arranged to protrude into female pockets provided in respectivesaid two of at least three surrounding housing elements.
 31. The axleassembly according to claim 30 wherein said bridging element iscylindrical and where each of said female pockets is semi-cylindrical inshape.
 32. An axle assembly according to claim 30 wherein said bridgingelement furthermore performs in the role of bearing to support saidmotor output shaft.
 33. An axle assembly according to claim 32 whereinsaid bridging element includes an intermediate portion and where saidintermediate portion is exposed exteriorly of said at least threesurrounding housing elements.
 34. The axle assembly according to claim17 wherein said bridging element includes an intermediate portion andwhere said intermediate portion is exposed exteriorly of said at leastthree surrounding housing elements such that said power transmissionlink is protected from exposure to the ambient environment.
 35. The axleassembly according to claim 17, further comprising at least one recessedpocket provided in one of said at least three surrounding housingelements, said recessed pocket overlying said bridging element.
 36. Theaxle assembly according to claim 35 wherein said bridging element iscylindrical and performs role of bearing to support said motor outputshaft.
 37. The axle assembly according to claim 36 wherein said bridgingelement includes an intermediate portion and where said intermediateportion is exposed exteriorly of said at least three surrounding housingelements.
 38. The axle assembly according to claim 37 wherein saidbridging element is in engaging contact with said at least one recessedpocket.
 39. The axle assembly according to claim 17 wherein any two ofsaid at least three surrounding housing elements are aluminium pressuredie-castings.
 40. The axle assembly according to claim 39 wherein theremaining at least one of said at least three surrounding housingelements is a pressed steel component.
 41. The axle assembly accordingto claim 39 wherein the remaining at least one of said at least threesurrounding housing elements is a plastic or nylon moulding.
 42. An axleassembly comprising a hydrostatic transmission and a differentialledgear reduction transmission disposed within at least three surroundinghousing elements, said hydrostatic transmission including a hydrostaticpump and motor and said differentialled gear reduction transmissionincluding a reduction gear train comprising a plurality ofinterconnecting gears, said hydrostatic transmission connected to saidreduction gear train by a power transmission link having a horizontalaxis of rotation disposed in a first horizontal plane and comprising amotor output shaft and a reduction gear train input shaft, a useroperated mechanical disconnect mechanism disposed intermediate saidmotor output shaft and said reduction train input shaft; a bridgingelement surrounding said motor output shaft and disposed adjacent saidmechanical disconnect mechanism, wherein at least two of said at leastthree surrounding housing elements are provided with uniplanar junctionseams meeting at a common parting plane arranged to be coincident withsaid first horizontal plane.
 43. The axle assembly according to claim42, and further comprising an input drive shaft having a vertical axisof rotation rotatably supported in one of said at least threesurrounding housing elements, said vertical axis of rotation of saidinput drive shaft disposed perpendicular to said first horizontal plane,wherein said input drive shaft comprises a first portion protrudingoutside of the respective housing element and a second portionprotruding inside of said respective housing element to drivingly engagesaid pump.
 44. The axle assembly according to claim 43, and furthercomprising a pair of axle shafts rotatably supported in at least two ofsaid at least three housing elements, said axle shafts having ahorizontal axis of rotation disposed parallel with said first horizontalplane.
 45. The axle assembly according to claim 44 wherein saiddifferentialled gear reduction transmission further comprising amechanical differential drivingly connected to said pair of axle shafts.46. The axle assembly according to claim 45, and further comprising acollar element disposed on respective ends of said motor output shaftand said reduction gear train input shaft, said collar element having alocked axial position where it is rotationally locked to said respectiveends of said motor output shaft and said reduction gear train inputshaft and an unlocked axial position where it is rotationally locked tothe end of only one of said motor output shaft and said reduction geartrain input shaft, said collar operationally connected to said useroperated disconnect member.
 47. The axle assembly according to claim 45wherein said horizontal axis of rotation of said axle shafts iscoincident with said first horizontal plane.
 48. The axle assemblyaccording to claim 47, and further comprising a bulkhead wall providedby at least one of said at least three surrounding housing elements,said bulkhead wall formed substantially vertically to be disposedgenerally parallel to the vertical axis of said input drive shaft, saidbulkhead wall delimiting an inner fluid reservoir surrounding saidhydrostatic transmission from an inner fluid reservoir surrounding saiddifferentialled gear reduction transmission such that said hydrostatictransmission is disposed one side of said internal bulkhead wall whereassaid differentialled gear reduction transmission is disposed on theopposite side.
 49. The axle assembly according to claim 47, and furthercomprising a collar element disposed on respective ends of said motoroutput shaft and said reduction gear train input shaft, said collarelement shiftable in one axial direction for drivingly connecting saidmotor output shaft to said reduction gear train input shaft and in theother axial direction for drivingly disconnecting said motor outputshaft from said reduction gear train input shaft, said collaroperationally connected to said user operated disconnect member.
 50. Theaxle assembly according to claim 49, and further comprising interiormounting surfaces disposed on a second horizontal plane in at least oneof said at least three housing elements; said hydrostatic transmissionfurther comprises a pintle-valve or centersection equivalent for fluidlycoupling said pump and motor together, said pintle-valve orcentersection equivalent fixed to said interior mounting surfaces,wherein said second horizontal plane resides parallel to and notcoincident with said first horizontal plane and said second horizontalplane positioned nearer said first portion of said input drive shaftthan said first horizontal plane.
 51. The axle assembly according toclaim 50 wherein only two of said at least three surrounding housingelements are aluminium pressure die-castings.
 52. The axle assemblyaccording to claim 50 wherein said motor output shaft is piloted to saidgear reduction train input shaft, the piloting of said motor outputshaft and said gear reduction train input shaft constituting thealignment mechanism of said power transmission link.
 53. The axleassembly according to claim 52 wherein said bridging element has a maleprofile arranged to protrude into female pockets provided in respectivesaid two of at least three surrounding housing elements.
 54. The axleassembly according to claim 53 wherein said bridging element iscylindrical and where each of said female pockets is semi-cylindrical inshape.
 55. An axle assembly according to claim 54 wherein said bridgingelement furthermore performs in the role of bearing to support saidmotor output shaft.
 56. An axle assembly according to claim 55 whereinsaid bridging element includes an intermediate portion and where saidintermediate portion is exposed exteriorly of said at least threesurrounding housing elements.
 57. The axle assembly according to claim42, wherein said bridging element includes an intermediate portion andwhere said intermediate portion is exposed exteriorly of said at leastthree surrounding housing elements.
 58. The axle assembly according toclaim 42, further comprising at least one recessed pocket provided inone of said at least three surrounding housing elements, said recessedpocket overlying said bridging element.
 59. The axle assembly accordingto claim 58 wherein said bridging element is cylindrical and performsrole of bearing to support said motor output shaft.
 60. The axleassembly according to claim 59 wherein said bridging element includes anintermediate portion and where said intermediate portion is exposedexteriorly of said at least three surrounding housing elements.
 61. Theaxle assembly according to claim 60 wherein said bridging element is inengaging contact with said at least one recessed pocket.
 62. The axleassembly according to claim 42 wherein any two of said at least threesurrounding housing elements are aluminium pressure die-castings. 63.The axle assembly according to claim 62 wherein the remaining at leastone of said at least three surrounding housing elements is a pressedsteel component.
 64. The axle assembly according to claim 62, whereinthe remaining at least one of said at least three surrounding housingelements is a plastic or nylon moulding.
 65. The axle assembly accordingto claim 42 wherein said differentialled gear reduction transmissionincludes a mechanical differential.
 66. The axle assembly according toclaim 42 wherein said hydrostatic transmission further comprises apintle-valve or centersection equivalent for fluidly coupling said pumpand motor together.